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Research has been conducted on the marine bacterium Pseudomonas nautica. The carbon dioxide rate in the bacterium's growth phases has been modeled via the bisubstrate enzyme kinetics, isocitrate dehydrogenase activity and intracellular isocitrate measurements and NADP (super)+, and the results are discussed.

Oceanic depth profiles of plankton respiration are described by a power function, ... similar to the vertical carbon flux profile. Furthermore, because both ocean processes are closely related, conceptually and mathematically, each can be calculated from the other. The exponent (FC), always negative, defines the maximum curvature of the respiration depth-profile and controls the carbon flux. When b is large, the C flux (FC) from the epipelagic ocean is low and the nutrient retention efficiency (NRE) is high allowing these waters to maintain high productivity. The opposite occurs when b is small. This means that the attenuation of respiration in ocean water columns is critical in understanding and predicting both vertical FC as well as the capacity of epipelagic ecosystems to retain their nutrients. The NRE is a new metric defined as the ratio of nutrient regeneration in a seawater layer to the nutrients introduced into that layer via FC. A depth-profile of F is the integral of water column respiration. This relationship facilitates calculating ocean sections of FC from water column respiration. In a FC section across the Peru upwelling system we found a FC maximum extending down to 400m, 50 km off the Peru coast. Finally, coupling respiratory electron transport system activity to heterotrophic oxidative phosphorylation promoted the calculation of an ocean section of heterotrophic energy production (HEP). It ranged from 250 to 500 Jd-1 m-3 in the euphotic zone, to less than 5 Jd-1 m-3 below 200m on this ocean section. [ABSTRACT FROM AUTHOR]

The dependence of growth, electron transport system activity and chemical composition on the size of diatoms was examined during the exponential phase of growth. The six different marine centric species compared ranged in volume from 77 μm[SUP3] to 62×10[SUP3] μm[SUP3]. A size dependence was observed for growth. ([SUP14]C uptake, respiration and the productively index ([SUP14]Clchl a). Although the size dependence of all parameters was similar, the results indicate that on a carbon basts, growth efficiency decreases with increasing size. The CIN and Clchl a ratios were not size dependent. The importance of the surface area to tell volume ratio, and the importance of carbon per unit volume in determining the observed size dependence are discussed. [ABSTRACT FROM AUTHOR]

In order to test the sensitivity of respiration (physiological and potential) to mercury (Hg) contamination, larval shrimp Pandalus borealis were exposed to inorganic Hg (0-160 ppb) for 27 h in the laboratory. Oxygen consumption rates (RO2), potential respiration (determined by respiratory electron transfer system activity, ETSA), protein content, and swimming activity for zoeae III and zoeae V stages were measured. For both zoeae stages, ETSA and protein content remained constant after 27 h exposure to 160 ppb Hg whereas RO2 and swimming activity decreased. This study revealed the impact of different Hg levels and different exposure times on RO2 of shrimp larvae. After 10 h exposure to 160 ppb Hg, the RO2 decreased by 43 and 49% in zoeae III and zoeae V stages, respectively. Exposure time of 27 h to 80 ppb Hg and higher, induced paralysis in nearly 100% larvae. Surprisingly, the paralysed larvae displayed almost 50% of the control's RO2. The results showed that Hg disturbs a part of the respiration process without modifying the maximum activity of the enzymes involved in the ETSA assay. Therefore, the ETSA assay can not be used as a sublethal bioanalytic probe to detect Hg in short-term exposures. The decline of the RO2/ETSA ratios reported here, indicates an inability of contaminated larvae to adapt their metabolism to physiological stress caused by Hg.

Variations of intracellular concentrations of isocitrate and NADP+ were measured throughout all growth phases of the marine bacterium Pseudomonas nautica. The intracellular isocitrate concentration tracked the intracellular protein concentration throughout all phases of growth. It rapidly increased in early exponential phase to a maximum and fell to nearly zero in parallel with pyruvate exhaustion in the culture medium. The intracellular NADP+ and protein concentrations increased in parallel during the exponential phase but were poorly correlated. Even after carbon exhaustion, the intracellular NADP+ concentration stayed high, as did protein levels. The results demonstrated that the intracellular isocitrate concentration, but not the intracellular NADP+ concentration, was affected by the carbon availability in the culture. They also suggest that, because of its variability, isocitrate, but not NADP+, plays the larger role in the control of the respiratory CO2 production rate (RCO2). From initial rate studies, bisubstrate Michaelis constants and the dissociation constant were determined for NADP+-specific isocitrate dehydrogenase (IDH) from P. nautica. These studies support the hypothesis that the mechanism of IDH's activity involves the ordered addition of the substrates, D-isocitrate and NADP+. Furthermore, the results support the use of a bisubstrate enzyme kinetic equation to model RCO2 in P. nautica.